Pennsylvania Gov. Tom Corbett, a Republican, is up for re-election in 2014. / Ralph Wilson, AP

by Catalina Camia, USA TODAY

by Catalina Camia, USA TODAY

The Republican made his comment in an interview that aired Friday, responding to a question about a statement made by state attorneys in court documents this summer. In the filing, Corbett administration lawyers compared gay and lesbian couples to children, noting that neither may legally marry in Pennsylvania.

"It was an inappropriate analogy, you know," Corbett said. "I think a much better analogy would have been brother and sister, don't you?"

The governor issued a statement Friday afternoon clarifying that he was trying to provide examples of the categories of individuals who are unable to obtain a marriage license under Pennsylvania law.

"My words were not intended to offend anyone. If they did, I apologize," Corbett said.

Democrats seized on Corbett's original comment and a video of the exchange on WHP-TV was uploaded by the Pennsylvania Democratic Party to YouTube. Vermont Gov. Peter Shumlin, chairman of the Democratic Governors Association, called Corbett's remark "an absurd comparison of same-sex marriage" to sibling incest that is "offensive and demeaning."

Corbett, who is up for re-election next year, has some of the lowest job-approval ratings in the country and is considered one of the most vulnerable incumbents in the 2014 elections. Public opinion polls show him trailing both U.S. Rep. Allyson Schwartz and state Treasurer Rob McCord, two of the better-known Democrats in the race, in head-to-head matchups.